The heating element assembly of this invention can be used in the same environment and for the same purpose as that of the heating element assembly of U.S. Pat. No. 4,687,905, dated Aug. 18, 1987, which issued to the same inventors, and can be formed in the same shape and equipped with the same kind of terminal block, although the terminal block used with the heating element assembly of this invention can be of simpler construction. Its use is not limited to that application, however. In the assembly of U.S. Pat. No. 4,687,905, a separate container or well was provided to house a thermal cut off assembly. This arrangement works well, but it is somewhat expensive and requires some additional wiring.
Attempts to house a thermal cutoff assembly within the sheath of a metallic sheathed electric heating element have heretofore been unsuccessful, because it has been thought that in order to get good thermal contact, it was necessary to position the thermal cutoff in contact with the pulverulent electrically insulating material that surrounds the resistance element. When that material was compacted, as it must be, the thermal cutoff assembly was damaged.
It has been discovered that if a two piece terminal pin is provided and the thermal cutoff assembly is positioned intermediate two sections of the terminal pin, within the compass of the sheath but spaced from the pulverulent insulating material, the sheath can be drawn down to compact the insulating material without damaging the thermal cutoff assembly, and at the same time, the thermal cutoff assembly will receive sufficient heat from the end of the section of pin to which the resistance element is connected, within the sheath, and, under overheating conditions, from the sheath itself, to provide an effective cutoff of the current to the resistance element if the heating element overheats, as in response to the running dry of a water heater tank, for example.
One of the objects of this invention is to provide a metallic sheathed electric heating element assembly, effectively protected by a thermal cutoff assembly, that is simpler, demands less space, and is more versatile than heating assemblies incorporating a thermal cutoff known heretofore.
Other objects will become apparent to those skilled in the art in the light of the following description and accompanying drawing.